In EUV lithography the position of the EUV producing plasma has to be stable within roughly a few tens of μm to ensure good imaging properties of the scanner. In a EUV radiation generating device like that known from WO 2005/025280 A2, the position of the emission center of the plasma is determined in two directions by the pointing stability of the trigger laser and in the third direction by the position of the electrode surface from which the metal melt is being evaporated by the same laser. However, this last position is not completely fixed in space since the electrode wheel heats up during operation and thus will expand in radial direction. Due to this the EUV hot spot (emission center of plasma) is shifted towards the other electrode. This would not be a problem in case of steady-state operation, as the position would be constant after a short time that is necessary to reach the thermal steady state. However, in a scanner as known from WO 2005/025280 A2 the light source is switched on and off on a similar time scale, so that the steady state will hardly be reached and the EUV producing plasma is moving continuously.
WO 2010/070540 A1 discloses a method and device for generating EUV radiation with enhanced efficiency using two lasers firing with a small time delay to evaporate the metal melt. The time delay between the two constrictive pulses, which are applied within a time interval of each electrical discharge, is varied in order to achieve a maximum EUV output.